The present invention relates generally to imaging procedures. More specifically, the present invention relates to methods and systems for imaging tissues surrounding arteries. The present invention is particularly, though not exclusively, useful for using intravascular ultrasound to profile an infiltration of a medicament into the tissue surrounding an artery.
Angioplasty is a widely used procedure for treating a stenosis within a body vessel such as a human artery. Although the angioplasty procedure is generally successful in dilating the lumen of the vessel, and thereby allowing increased blood flow through the vessel, often times a restenosis occurs soon after the angioplasty procedure. It is widely recognized that the body""s response (inflammation). to the tissue damage that occurs during an angioplasty procedure contributes to the occurrence of a restenosis. Several medicaments, however, are known to be efficacious for the prevention of a restenosis if properly delivered near the site of the inflammation. To that end, devices that are capable of penetrating the wall of a vessel with a dispenser and releasing a medicament into the vessel wall have been developed. For example, U.S. Pat. No. 5,713,863 which issued to Vigil et al. for an invention entitled xe2x80x9cCatheter With Fluid Medication Injectors,xe2x80x9d and which is assigned to the same assignee as the present invention, discloses such a device. It is the case, however, that these intravascular infusion devices can be used to deliver medicaments for prevention of restenosis as well as for other treatment and diagnostic purposes.
There are various forms of tissue injury that can result from an intravascular procedure, any one of which will trigger an inflammation response. As indicated above, such an inflammation response is widely recognized to contribute to the restenosis of the vessel. It is also known that this inflammation response will cause localized changes near the injured tissue including increased permeability and increased blood flow. This localized increase in blood flow and permeability will generally increase the dispersion rate of medicaments released near an injury in a vessel wall.
For a medicament to be effective in preventing a restenosis it must be delivered to a prescribed area and in a prescribed dosage. To do this efficiently, the size, shape and location of the prescribed treatment area must be determined, and this will depend on the amount and location of tissue injury. Also, the dispersion rate of the medicament will be affected by the amount of inflammation, the type of medicament, and the amount of medicament released. Due to the many variables involved, it would obviously be helpful to know exactly where the medicament has dispersed into tissue after it has been administered.
It happens that results of an intravascular infusion procedure are not the same from patient to patient. This may be due to a variety of reasons. One possible reason is the anatomical differences between patients. The differing results can also be due to different degrees of inflammation of the tissues, as discussed above. In any event, the actual distribution of the medicament has been a matter of estimate, based on clinical results. Heretofore, there has been no reliable in-vivo method to ascertain the success of an intravascular infusion procedure. Thus, it can be appreciated that it would be beneficial to know whether the medicament actually reached the target tissue. It would also be desirable to know whether the infused medicament is uniformly distributed in the target area. Of further interest to a clinician would be the concentration of the infused medicament in the tissues surrounding the arterial wall.
Information regarding the condition of tissues inside a patient can be obtained using diagnostic radiology. In particular, diagnostic ultrasound techniques can give information about tissue condition by differentiating between tissues at their anatomic boundaries inside the patient. Specifically, this happens as transmitted ultrasound waves reflect back to the transducer from these boundaries. The amplitude of the reflected ultrasound waves is then displayed as different shades of gray. Thus, anatomic structures with different acoustic density will be portrayed with different brightness. The introduction of a medicament into a tissue, however, changes its videodensitometry. Importantly, an ultrasonic image can show this difference.
Ultrasound technology is now available which will produce an inside view of an artery. Specifically, intravascular ultrasound, or IVUS, incorporates an ultrasound head within: a balloon catheter which can be used to obtain a cross sectional image of an artery. This image will also include the tissue that is surrounding the artery. An example of the use of IVUS can be found in the detection of plaque inside artery walls. Another example is the use of IVUS to determine the position and orientation of a probe during a procedure, using perivascular structures as landmarks.
In light of the above, it is an object of the present invention to provide a reliable method for profiling an infiltration of a medicament into the tissue surrounding an artery. Another object of the present invention is to provide a method and a system to determine the extent of the infiltration of the medicament into an arterial wall of a patient. A further object is to provide a system for quantitatively evaluating the distribution of the medicament in the tissue surrounding the artery. Yet another object of the present invention is to provide a method for profiling the infiltration of a medicament into the tissue surrounding the artery that is easy to perform, is safe, and is comparatively cost effective.
The present invention is directed to a method for determining the extent of an infiltration of a medicament into an arterial wall of a patient. Essentially, this is a two-step process. First, the medication is administered. Second, the extent of medication infiltration is determined. In accordance with the present method, a balloon catheter infusion device containing the fluid medicament is positioned in the artery of the patient at the treatment site. Upon being so positioned, the device then injects the medicament from inside the lumen of the artery into the wall of the artery. As the medicament is released, it infiltrates into the tissue surrounding the artery. It is anticipated that this procedure can be accomplished either at only one treatment site or repeated at a number of locations along the wall of the artery. This, of course depends on the pathology of the artery. In detail, when multiple infusions are to be performed, the infusion device is first advanced to a position in the artery that is most distal from the point of entry for the device. The device is then gradually pulled back through the artery, and the medicament is injected into selected sites along the arterial wall. When the infusion process is completed, the balloon catheter housing the infusion device is withdrawn from the artery.
In accordance with the present invention, after the infusion device has been withdrawn, another catheter is inserted into the lumen of the artery. This second catheter houses an intravascular ultrasound device (IVUS) of a type well known in the pertinent art. The IVUS is then advanced to the location of the infusion that is most distal from the point of entry of the device. The ultrasound is activated, and it begins imaging the arterial wall at a start point.
From this start point, the device is incrementally withdrawn, through the artery. This is preferably done using a motorized pullback device which will stabilize the IVUS in an axial orientation as it takes images of the artery between its incremental movements through the artery.
As the IVUS is thus pulled back along the axis of the artery, it creates a series of images at predetermined or preselected positions in the artery.
Each image, thus created, will represent the extent of medicament perfusion at a specific axial position in the artery. Once the ultrasound has created a profile of the tissue surrounding the artery, at the various axial positions in the artery, the IVUS is removed from the artery. It is known that IVUS, in general, provides a cross sectional view of the inside of an artery and the tissues immediately surrounding the artery. Thus, these images that are created at the series of specific axial sites in the artery, will each include a radial and an azimuthal dimension. The present invention envisions a computer/ultrasound interface that is capable of combining all of these images to produce a three dimensional image of the tissue surrounding the artery.
In operation, the specific sites for creating images with the IVUS are based on the location of the infusion. As indicated above, it is contemplated that multiple images will be created at a given infusion site. It then follows that, if a medicament has been infused at more than one site, each infusion site will be imaged a number of times. Further, at each infusion site it is desirable to know the boundaries of the perfusion or infiltration of a medicament. For diagnostic purposes, these boundaries will include a first end, the radial extent of the perfusion through an azimuthal range, and a second end. These measurements will then represent the extent of penetration of the medicament into the tissue surrounding the artery. Preferably, a minimum of three sites along the arterial wall at each infusion site will be selected for imaging with the IVUS. This determination will be repeated for each infiltration that has been performed.
In detail, and taking into account that IVUS generates images from specific axial positions in the artery, radial and azimuthal dimensions can be ascertained for each position. These dimensions correspond to the boundaries of the perfusion at each position. Beginning at a first position, the start point, a first image is created by the IVUS in a manner known in the art. When a clinician determines that this image represents the distal point of the perfusion of the medicament, at least two other axial positions are selected for imaging the perfusion. Accordingly, the pullback device incrementally withdraws the IVUS and pauses at a second position, a predetermined distance from the position of the first image. A second image is created at this second position. Once again, the pullback device is activated, and the IVUS is withdrawn to a third location along the artery. The imaging procedure is repeated, creating a third image. It can be appreciated that the clinician could select a greater number of sites depending on the specificity of the information desired. For instance, if images are created at increments of one to three millimeters along the artery at a given perfusion site, more than three images will be needed to observe the entire perfusion in detail. Consequently, the profile generated from the combined images will be more detailed than a corresponding profile generated from three images. In any event, the clinician can determine the number of images to be made based on observations of the image created at the first position. When the desired number of images has been made at the first infusion site, the IVUS is pulled back along the axis of the, artery. Accordingly, if additional infusions were made, a series of images is created at each infusion site. Upon the completion of the desired number of images at each location of perfusion, the IVUS is withdrawn from the artery.
In addition to creating images at specific sites along the inside of the artery, the present invention envisions using these images to quantify the results of the infusion. An important aspect of the present invention is an analysis of the profile created by the ultrasound. It is known that tissues with varying characteristics react differently to ultrasound radiation to produce images showing this variation. As noted above, the addition of a medicament to tissues changes the characteristics of the tissues containing the medicament for the purpose of creating an ultrasound image. Consequently, the tissues that contain the medicament will have a profile that differs from the profile of those tissues that do not contain the medicament. Based on this understanding, a quantitative analysis of the images can be performed to determine the relative amount of the medicament that has infiltrated into selected areas of tissue. Specifically, to accomplish this, data from the series of images is combined at an ultrasound/computer interface. It is known that each of the combined images-includes a radial and an azimuthal dimension of the perfusion. Accordingly, the composite of these images will yield a three dimensional image of each perfusion. Supported by these composite, three dimensional images, and the quantitative analysis of these images, a clinician can evaluate the pattern and the extent of the infiltration of the medicament.